PORTSMOUTH — Two crew members escaped from a rapidly sinking tugboat Wednesday after it became pinned against a barge at the Memorial Bridge construction site and capsized.

The U.S. Coast Guard, New Hampshire Marine Patrol and Portsmouth Fire Department responded to the scene when the tugboat began to sink at about 11:45 a.m.

An employee of a nearby construction site said the boat sank within minutes after it tipped over and began taking on water.

The Benjamin Bailey, the 1,200-horsepower tugboat, was working under contract with Archer Western Contractors, the company running the Memorial Bridge project.

The tugboat is owned by Riverside and Pickering Marine Contractors in Eliot, Maine, and was staffed by local crew members who have knowledge of the area, according to Archer Western spokeswoman Carol Morris.

The accident occurred about two hours before low tide, a time during which the river current in the area would have been at a high point in the tidal cycle, according to Coast Guard Lt. Nick Barrow.

A video of the accident shows the 55-foot boat pinned up against the barge, being swept sideways by the waves. A crew member can be seen leaping from the overturned cabin and onto the barge.

Salvage crews were preparing to lift the ship from the water in the afternoon during the slack tide, but the effort was eventually called off for the evening.

The ship is loaded with an unknown quantity of diesel fuel, Barrow said. The ship's owner has reported the tanks were not entirely filled when the ship went down.

Efforts to salvage the ship will likely resume this morning, at the discretion of the boat owner and the New Hampshire Department of Environmental Services, Barrow said.

The ship, which is resting at the bottom of the river, has been secured to the barge in multiple locations to secure it overnight, Barrow said.

Salvaging the tug will likely take two phases: first, crews will need to pump the water out of the hull; second, it must be towed to a different location to be inspected and removed from the water.

Morris said the owner of the boat is considering using inflatable air bags to lift the ship back to the surface, but the exact method hasn't been determined yet.

The Coast Guard, which is investigating the accident, has yet to determine the cause. Barrow said there were at least two — and possibly three — crew members on board when the accident happened. They have provided statements, and are cooperating with the Coast Guard, Barrow said.

Morris said it doesn't appear the tugboat was engaged in a specific work function when it sank.

“We don't know why it went down yet,” Morris said. “Obviously there's going to be an investigation.”

Staffers from the NHDES were also on hand in Portsmouth Wednesday afternoon.

DES Public Information Officer Jim Martin said there were no indications that material was leaking from the ship into the river as of 2 p.m.

Reached in the early evening, Barrow said the Coast Guard has observed a small amount of material bubbling up from the tugboat and creating a light sheen on the water.

“We're on scene doing what we can to capture anything we can that is released from the boat using absorbent booms,” Barrow said.

Barrow said the Coast Guard planned to remain at the accident scene until the early evening. The owner of the tug was also planning to make someone available to monitor the ship, he said.